The present invention relates to a shaft for an open-end spinning rotor, the free end of which shaft comprises a supporting element which is arranged in a concentric recess of the shaft, said supporting element having an essentially radially extending supporting surface for a vibrating ball of a step bearing.
It is known (U.S. Pat. No. 5,349,809) that a cylindrical pin is used as a supporting element and is arranged in a concentric recess of the shaft. The pin has an essentially radially extending supporting surface, with which it is supported on a vibrating ball of the step bearing. When the pin is inserted into the recess, the air present there must be displaced. The pin is therefore provided in a first variation with longitudinal grooves, by means of which the displaced air can escape to the outside. In another variation, the recess adjoins an additional hollow space, in which the air displaced from the recess is compressed.
It is known (German published patent application 19 01 453) that a supporting element is used which has the shape of a hemisphere, a section of which projects from the front end of the shaft. The supporting element is supported on a stationary, essentially plane component of the step bearing.
The problems with the displacement of air can be avoided to a great extent when instead of a pin a ball is used as a supporting element. However, the use of a ball as a supporting element of a shaft can cause new problems in the case of step bearings which comprise a vibrating ball for the disposed shaft. If the axis of the shaft does not exactly align with the ball of the step bearing, it can lead to a displacement of the axial position of the open-end spinning rotor and to undesirable radial movements of the shaft, in particular to a radial migration. Even small deviations in tolerance in the manufacture of the step bearing are sufficient to bring this about.
In order to achieve faultless spinning results it is very important that the rotor cup attached to the shaft continuously takes up an exact, predetermined axial and radial position. When not exactly aligned, the center point of the vibrating ball is displaced relative to the axis of the shaft, so that the ball-shaped supporting element lies eccentric thereto. The position of the rotor cup is then displaced in the direction of the step bearing. This results in a change in the geometrical arrangement in the spinning area. The feeding of fibers into the rotor cup does not take place at the intended place, and the withdrawal nozzle is too far away from the rotor cup.
The change in the geometrical arrangement results in an increase in end-breaks and a worsening of yarn quality, in particular with respect to strength and evenness. In addition, the eccentric position of the ball-shaped supporting element effects an uneven axial and radial operation of the open-end spinning rotor. This also has a negative effect on the spinning results.
It is an object of the present invention to provide in the case of a shaft for an open-end spinning rotor an easily installed supporting element which does not adversely affect the predetermined axial and radial position of the open-end spinning rotor.
This object has been achieved in accordance with the present invention in that the supporting element is formed by a ball which projects out of the recess with a radially flattened section which contains the supporting surface.
A supporting element in the shape of a ball can be inserted into the shaft recess without any great difficulty. As, during insertion, the ball-shaped supporting element is disposed against the peripheral side of the recess with only a line extending in circumferential direction, the greater part of the air along the line can escape from the recess. With application of the usual tools for manufacturing the recess, it obtains a form such that the supporting element is not disposed against the entire peripheral surface of the recess, which leaves enough space for a possible compression of air.
Due to the radially extending supporting surface of the ball as a result of flattening, the contact surface, with which the supporting element touches the ball, extends also radially to the shaft. An axial displacement of the open-end spinning rotor is thus avoided. Also, radial forces at the step bearing, which could lead to undesirable migration and an uneven operation of the shaft, do not arise.
The supporting element can be arranged in the recess in different ways. The supporting element can, for example, be secured inside the recess by means of a suitable adhesive. Furthermore, it is also possible to use holding means which are effective from outside of the recess.
In an advantageous embodiment, the supporting element is made by removing material from the ball, for example by means of grinding. It is hereby advantageously possible to apply the supporting surface then when the supporting element has been inserted into the recess. It is also possible to insert the supporting element in its final form into the recess and for insertion to dispose it on its plane supporting surface.
The ball is made of a harder material than the vibrating ball and/or the shaft. The ball can be advantageously made of ceramic material.
In an advantageous embodiment, the recess has a stopping face for axially fixing the ball. It is hereby advantageous when the recess comprises a hollow conical section, whose peripheral surface forms the stopping face. Such a hollow conical section can be produced easily when the recess is manufactured using a drill.
In an advantageous way, the ball is held in the recess by means of a press fit.
In an advantageous embodiment the shaft is hardened at least in the area which borders the recess. Thus a widening of the shaft when pressing in the ball is avoided.
According to certain preferred advantageous embodiments, the supporting ball is received in a cylindrical bore of the shaft which has been extended by a bore with a smaller diameter. In this advantageous embodiment, the material which is removed from the ball is dimensioned so that the ball projects only approximately 0.4 mm beyond the end of the shaft. Also in this embodiment, the shaft is hardened to approximately 40 Rockwell hardness in the vicinity of the end of the shaft, which thereby prevents expansion of the shaft when the ball is pressed in and when the bore for accommodating the ball is produced.
In accordance with especially preferred embodiments of the method for manufacturing the rotor shaft assembly, the receiving bore for the supporting ball is drilled in the shaft after the shaft has been hardened.
According to advantageous features of preferred embodiments of the invention, the supporting surface of the ball projects with its supporting surface by an amount of no more than 1 mm beyond the end of the shaft. This ensures that the ball is largely protected during transportation and handling, so that alignment of the radial supporting surface of the ball is not altered inadvertently.
According to especially advantageous embodiments of the method of making the assembly, the ball is first placed in the bore and then fastened there, and thereafter the ball is machined to produce the supporting surface. Since the shaft and the ball form a unit before the supporting surface is produced, there is no problem to produce the supporting surface exactly radially to the shaft axis. In especially preferred embodiments, the supporting surface on the ball is formed following insertion of the ball in the receptacle of the shaft by grinding away the material of the ball. With the shaft being hardened, at least in the vicinity of the shaft end to a hardness of 40 Rockwell or more, the deformation that would otherwise be caused to the shaft when the ball is pressed in is limited.
Objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.